The invention relates to a device for introduction of gases into reaction vessels containing liquids, especially vessels undergoing thermal stress, in particular filter housings for metal melts, by means of a gas-permeable body of heat-resistant material, fitting into a metal sleeve, which itself is anchored in the wall of the reaction vessel.
Since the introduction of methods for treatment of metal melts, in which gases are continuously injected into the melt, it has been found difficult to secure the gas-permeable inlet bodies of heat-resistant material in the wall of the reaction vessel in an easily exchangeable but nevertheless leak-tight-manner. In view of the state of the art, an attempt have therefore focussed to build in the inlet body permanently into the wall of the vessel, the latter consisting of concrete or similar materials. However, this solution leads to the significant disadvantage that, upon the periodical exchange of inlet bodies, the relevant wall of the reaction vessel has to be totally destroyed, which in turn is unduly costly causes a significant loss of time, and reduces the operating working time of the relevant reaction vessel in a significant way.
Therefore, a further attempt has been made to facilitate the exchange of the inlet body, by surrounding the inlet body with a metal sleeve, and by anchoring the latter in the wall of the reaction vessel.
The objective aimed at was, however, not satisfactorily achieved in this way, since undesired side effects arose causing severe disadvantages compared to the conventional installation of the inlet body, namely tightness of the device with a view to prevent any leaks could not be significantly improved by the use of the metal sleeve, and any undesired loss of gas could not be effectively eliminated; compared to a brick built-in directly into the wall, a device consisting of an inlet body, a metal sleeve and a wall has significantly greater differences in the coefficient of thermal expansion of the various materials present in the system. If the inlet body, substantially in accordance with the proposals of U.S. Pat. No. 2,811,346 of U.S. Pat. No. 2,947,527, is, however, rigidly anchored by means of screws to the metal sleeve, then the metal sleeve expands significantly more than the inlet body upon heating up of the device by the metal melt. Therefore, a gap arises between sleeve and inlet body, through which the gas escapes, or into which the liquids from the reaction vessel can pass, if no excess gas pressure prevails in the gas inlet body.
The use of a metal sleeve between the inlet body and the wall of the reaction vessel leads to the further disadvantage that the metal sleeve ifself, by the combination of thermal and chemical effects, is prematurely damaged, and that the liquid in the reaction vessel is polluted by metal material of the sleeve. This is especially undesired, if the device is used to treat highly purified metal melts. The direct contact between the metal of the sleeve and the contents of the filter housing, and the corrosion thereby arising severely constrains a more widespread use of the device at an prevents it from being applied to the injection of gas into chemically corrosive liquids, as for example strong acids, an elevated temperature.
Neither has a satisfactory solution of the problem of easy exchangeability been achieved yet in the present state-of-the art, although devices have been designed, in which the metal sleeve is fastened by means of screws to the outer wall of the reaction vessel (U.S. Patent Specification 2,871,008, FIG. 5). But the designer of that device has not taken into account the fact that the metal sleeve, being an excellent thermal conductor, is in direct contact with the hot liquid in the interior of the filter housing, and that during the operation of the installation a steep temperature gradient may therefore occur along the longitudinal axis of the sleeve. The thermal expansion of the sleeve in its longitudinal direction exceeds that of the material of the wall of the reaction vessel surrounding it, or of that of the inlet body. This in turn, leads to a dislocation of the sleeve with respect to its surroundings, and if, it is firmly anchored both in the wall and in the steel casing of the reaction vessel, as indicated in U.S. Pat. No. 2,871,008 FIG. 5, this might lead to mechanical tensions, if not cracks. An improvement in devices for the introduction of gases into reaction vessels containing fluids is also disclosed in co-pending application Ser. No. 649,137; additional pertinent references are U.S. Pat. No. 3,343,829, disclosing a porous plug assembly for a metallurgical receptacle, U.S. Pat. No. 3,834,685, teaching an apparatus for injecting fluids into molten metals, and British Pat. Specification No. 697,915, relating to improvements in Ladles for Gas Flushing Molten Metal. The advantageous combination of a substantially air-tight shell of ceramic material secured to the side surface of an inlet body and a loose intermediate layer of bulk material included in the wall of the reaction vessel has not been found in the prior art.